Field of the Invention
The invention relates to a memory and particularly relates to a resistive memory and a resistance window recovery method for a resistive memory cell thereof.
Description of Related Art
Resistive random access memory (RRAM) is a type of non-volatile memory. RRAM can retain or store values by changing the resistance state. A resistive memory has excellent compatibility with the integrated circuit manufacturing process. The resistive memory has a high write speed and the write voltage is lower, which meets the low power consumption requirement of portable electronic products.
In the resistive memory, the three operations, i.e., forming, set, and reset, are three important steps for ensuring the electrical characteristics and data retention of the resistive memory cell. During the set/reset operation, the input voltage may need to be raised gradually and repeatedly, which is the so-called ramping operation. For some problematic memory cells, if an overly high voltage is used to perform the reset operation (or set operation) of the resistive memory cell, it may increase the current of the resistive memory cell that should be in a low current state (or reduce the current of the resistive memory cell that should be in a high current state). This phenomenon is called complementary switching (CS). The CS phenomenon is a unique phenomenon to the field of resistive memory.
Once the CS phenomenon occurs in the resistive memory cell, the resistance window (or called voltage window) of the reset operation of the memory cell will be narrowed (or even disappear). When “the resistance window is narrowed,” it means that high resistance state HRS and low resistance state LRS will become difficult to distinguish. In other words, the memory cell will lose memory capability. Therefore, it is important to prevent the CS phenomenon when performing the set operation and the reset operation for the resistive memory cell. Nevertheless, the endurance of the resistive memory cell is limited. As the number of times of performing the operations (reset and/or set) increases, it is inevitable for the resistive memory cell to encounter the CS phenomenon. Thus, when the CS phenomenon occurs, how to recover the resistance window of the resistive memory cell is an important issue.